1. Field of the Invention
This invention relates to a semiconductor light-emitting device. This semiconductor light-emitting device can be utilized as a light-emitting diode, a laser diode, or the like.
2. Description of the Conventional Art
Light-emitting devices using compound semiconductors cover visible short wavelength regions. Among other light-emitting diodes, nitride III semiconductors have attracted attention in recent years because these semiconductors are direct transition semiconductors, so that they exhibit high light-emitting efficiency, and because these semiconductors emit blue light, which is one of the three primary colors.
When the light-emitting layer is formed of In.sub.X Ga.sub.1-X N, it has heretofore been considered that a relation such as shown by the dashed line in FIG. 1 exists between the indium mole fraction X and the photon energy (see "Journal of applied physics", Vol. 46, No. 8, August 1975, pp. 3432-3437 and "Microelectronics Journal", 25 (1994), pp. 651-659). The photon energy of the wavelength .lambda. of blue light (470 nm) is almost 2.64 eV, and the photon energy of the wavelength .lambda. of green light (520 nm) is almost 2.38 eV. Therefore, according to the conventionally proposed relation, blue emission is obtained by setting the indium mole fraction X to approximately 0.26 and green emission is obtained by setting the indium mole fraction X to approximately 0.67 if no impurities are to be added.
As a result of a continued study on the light-emitting layer formed of In.sub.X Ga.sub.1-X N, the inventors realized that the conventionally proposed relationship shown by the dashed line in FIG. 1 could not be applied without modification if such a light-emitting layer is to be formed on a sapphire substrate.